A steering angle sensor detects a steering angle of a steering wheel of a vehicle and provides a signal necessary for a vehicle control system to calculate an absolute steering wheel angle from the detected signal. When the vehicle is not in use, the ignition switch is powered off, there is typically no power provided to the steering angle sensor, as it is typically assumed that the steering wheel will remain stationary. However, in rare instances, the steering wheel is turned when the vehicle is powered off, and many vehicle control systems need to know the absolute steering wheel angle upon power-on of the ignition switch. Therefore, a discrepancy between the steering wheel angle sensed at power-off will be present in comparison to the steering wheel angle sensed at power-on.
In order to combat this problem, some solutions provide power to the steering angle sensor, regardless of the state of the ignition switch, from the vehicle's battery. However, since the sensor is always powered-on, the amount of battery power consumed when the ignition is off. Another solution is to store a learned angle and power-off and retrieve the angle as a tentative angle at key-on until the vehicle moves resulting in confirmation or rejection of the tentative angle as the absolute steering angle.
Another alternative is that the steering wheel angle sensor periodically detects the steering angle of the steering wheel when the vehicle's ignition is off. Thereby, conserving power. However, intermittent power introduces the likelihood that a signal will be missed should a steering wheel angle change during a period of no power and may not be a reliable solution.